nir: Lower subtraction to add with negation when !lower_negate.

prog->nir will generate fsub opcodes, but i965 doesn't implement them.
We may as well lower them at the NIR level, since it's trivial to do.

Suggested by Connor Abbott.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index 20ec4d3..66b456d 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -161,6 +161,8 @@ optimizations = [
    # Subtracts
    (('fsub', a, ('fsub', 0.0, b)), ('fadd', a, b)),
    (('isub', a, ('isub', 0, b)), ('iadd', a, b)),
+   (('fsub', a, b), ('fadd', a, ('fneg', b)), '!options->lower_negate'),
+   (('isub', a, b), ('iadd', a, ('ineg', b)), '!options->lower_negate'),
    (('fneg', a), ('fsub', 0.0, a), 'options->lower_negate'),
    (('ineg', a), ('isub', 0, a), 'options->lower_negate'),
    (('fadd', a, ('fsub', 0.0, b)), ('fsub', a, b)),